Altitude deviation on descent.

Attributes
ACN	295310
Time
Date	199501
Day	Wed
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : mei
State Reference	MS
Altitude	msl bound lower : 27750 msl bound upper : 28000
Environment
Flight Conditions	VMC
Light	Dusk
Aircraft 1
Controlling Facilities	artcc : zme
Operator	common carrier : air carrier
Make Model Name	MD-88
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	descent other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : atp
Experience	flight time last 90 days : 95 flight time total : 6200 flight time type : 1200
ASRS Report	295310
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : overshoot non adherence : clearance
Independent Detector	aircraft equipment other aircraft equipment : unspecified other flight crewa
Resolutory Action	flight crew : overcame equipment problem flight crew : returned to intended course or assigned course
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	Pilot Deviation

Narrative:

Having received clearance to FL280, the captain programmed the FMS to descend to FL280 by a point 35 mi west of mei. The aircraft started the descent early, so the captain changed from an FMS descent to a vertical speed descent. At this time 'altitude arm' light was illuminated for altitude capture at FL280. At approximately 250 ft below FL280, the altitude warning horn sounded at which time the descent was stopped and the aircraft was returned to FL280. No conflict was noted. Standard callouts were accomplished. Callback conversation with reporter revealed the following information: the reporter flies the md-88 for a major united states air carrier. He likes the aircraft and calls it 'an old aircraft with new software.' he thinks this episode was primarily a 'software problem.' he agrees that he should have been watching the aircraft more closely. The aircraft has made him more aware and watchful. There was no word from ARTCC. It is highly probable that the controller did not notice. The reporter's air carrier's policy is to avoid changing the altitude mode within the last 1000 ft of capture so as to avoid losing the altitude capture feature. The crew did not change the altitude mode.

Original NASA ASRS Text

Title: ALTDEV ON DSCNT.

Narrative: HAVING RECEIVED CLRNC TO FL280, THE CAPT PROGRAMMED THE FMS TO DSND TO FL280 BY A POINT 35 MI W OF MEI. THE ACFT STARTED THE DSCNT EARLY, SO THE CAPT CHANGED FROM AN FMS DSCNT TO A VERT SPD DSCNT. AT THIS TIME 'ALT ARM' LIGHT WAS ILLUMINATED FOR ALT CAPTURE AT FL280. AT APPROX 250 FT BELOW FL280, THE ALT WARNING HORN SOUNDED AT WHICH TIME THE DSCNT WAS STOPPED AND THE ACFT WAS RETURNED TO FL280. NO CONFLICT WAS NOTED. STANDARD CALLOUTS WERE ACCOMPLISHED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR FLIES THE MD-88 FOR A MAJOR UNITED STATES ACR. HE LIKES THE ACFT AND CALLS IT 'AN OLD ACFT WITH NEW SOFTWARE.' HE THINKS THIS EPISODE WAS PRIMARILY A 'SOFTWARE PROB.' HE AGREES THAT HE SHOULD HAVE BEEN WATCHING THE ACFT MORE CLOSELY. THE ACFT HAS MADE HIM MORE AWARE AND WATCHFUL. THERE WAS NO WORD FROM ARTCC. IT IS HIGHLY PROBABLE THAT THE CTLR DID NOT NOTICE. THE RPTR'S ACR'S POLICY IS TO AVOID CHANGING THE ALT MODE WITHIN THE LAST 1000 FT OF CAPTURE SO AS TO AVOID LOSING THE ALT CAPTURE FEATURE. THE CREW DID NOT CHANGE THE ALT MODE.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.